This invention relates to a method and apparatus for generating vapor, more particularly steam or vapor suitable for use in an electric power generating plant in which water or low boiling point liquid such as freon is vaporized by using subground hot water or industrial hot or warm waste water or flue hot gas and the resulting steam is utilized to drive a steam or vapor turbine.
In the prior art geothermal electric power generation plant, only steam collected from subground was used and subground hot water was not utilized efficiently. In recent years, use of thermal energies at a relatively low temperature such as the subground hot water and industrial hot water for generating steam has become important. In such apparatus for generating steam or vapor, a heat exchanger is provided to heat water by relatively low temperature hot water or low boiling point liquid such as freon to generate steam for driving a steam turbine coupled to a generator.
FIG. 1 shows a prior art steam generating apparatus or heat exchanger utilized for this purpose which comprises a cylindrical vessel 1 provided with a hot water (R.sub.L) inlet port 1a on the lower side at one end and an exit port 1b for discharging generated steam R.sub.V on the upper side and at the other end. The opposite ends of the vessel 1 are closed by header plates 2 and 3 between which a plurality of heat transfer tubes 4 extend. The header plates 2 and 3 are covered by cup shaped end plates 5 and 6. The interior of the end plate 5 is divided by a partition plate 7 into upper and lower compartments. The lower compartment is provided with an inlet port 5a for hot water W, whereas the upper compartment is provided with an exit port 5b for the used hot water. Thus, the hot water W flows from the inlet port 5a, lower heat transfer tubes 4, a chamber within the righthand end plate 6, upper heat transfer tubes 4 and finally discharged from the exit port 5 b, as shown by arrows. On the other hand the water R.sub.L to be evaporated flows about the heat transfer tubes 4 and the resulting steam R.sub.V is discharged through the exit port 1b.
Since this type of steam generator utilizes a pool boiling phenomenon, heat transfer coefficient is low with the result that the thermal energy of the hot water is not used efficiently, thus requiring a large amount of the hot water or large heat transfer surface.
Consequently, it has been desired to develop an efficient and compact steam generator utilizing relatively low temperature hot water as subground hot water or industrial hot waste water.